1. Field of the Invention
The invention relates to a device for recycling of molding sand after it is used in a sand casting process.
2. Description of the Related Art
Molding sand, also known as foundry sand, is sand that tends to pack well and hold its shape. It is used in the process of sand casting.
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term “sand casting” can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via a sand casting process.
Sand casting is relatively cheap and sufficiently refractory even for steel foundry use. In addition to the sand, a suitable binder is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances, to develop strength and plasticity of the clay and to make the aggregate suitable for molding. The sand is typically contained in a system of frames or mold boxes known as a flask. The mold cavities and gate system are created by compacting the sand around models, or patterns, or carved directly into the sand.
There are four main components for making a sand casting mold: base sand, a binder, additives, and a parting compound.
Binders are added to a base sand to bond the sand particles together (i.e. binders are the “glue” that hold the mold together).
A mixture of clay and water is the most commonly used binder. There are two types of clay commonly used: bentonite and kaolinite, with the former being the most common.
Oils, such as linseed oil, other vegetable oils and marine oils, used to be used as a binder, however due to their increasing cost, they have been mostly phased out. The oil also required careful baking at 100 to 200° C. (212 to 392° F.) to cure (if overheated the oil becomes brittle, wasting the mold).
Resin binders are natural or synthetic high melting point gums. The two common types used are urea formaldehyde (UF) and phenol formaldehyde (PF) resins. PF resins have a higher heat resistance than UF resins and cost less. There are also cold-set resins, which use a catalyst instead of a heat to cure the binder. Resin binders are quite popular because different properties can be achieved by mixing with various additives. Other advantages include good collapsibility, low gassing, and they leave a good surface finish on the casting. MDI (methylene diphenyl diisocyanate) is also a commonly used binder resin in the foundry core process.
Sodium silicate [Na2SiO3 or (Na2O)(SiO2)] is a high strength binder used with silica molding sand. To cure the binder carbon dioxide gas is used.
The advantage to this binder is that it occurs at room temperature and quickly. The disadvantage is that its high strength leads to shakeout difficulties and possibly hot tears in the casting.
The sand casting process progresses as follows. First, a pattern in placed in the molding sand to create a mold. Second, the pattern and the molding sand are incorporated in a gating system. Third, the pattern is removed. Fourth, the mold cavity is filled with molten metal. Fifth, the metal is allowed to cool. And sixth, the sand mold is broken away and the metal casting is removed.
While the metal casting produced in the sand casting process is the desired product, it is also beneficial to recycle the molding sand by separating off the binders, adhesives, and parting compounds so that the recycled sand particles can be reused for making sand casting molds.
Conventional methods of recycling molding sand make use of dry, vibratory reclamation to produce intensive abrasions designed to grind off layers of old binders, adhesives, and parting compounds, and to separate them from sand grains.
Various types of conventional sand reclaiming devices are known. However, in addition to being overly complex and expensive to build, conventional sand reclaiming devices direct vibrations rectilinearly to be coincident with the main direction of sand shifting. This limits the pathway along which abrasive effect is applied. Clearly, much opportunity remains for improvement in this area of technology.